1. Field of the Invention
The present invention relates generally to the field of reactivity compensation methods for nuclear reactors and, in particular to a method for fail-safe reactivity compensation in solution-type nuclear reactors. In one embodiment, the fail-safe reactivity compensation method of the present invention augments other control methods for a nuclear reactor. In still another embodiment, the fail-safe reactivity compensation method of the present invention permits one to control a nuclear reaction in a nuclear reactor through a method that does not rely on moving components into or out of a reactor core, nor does the method of the present invention rely on the constant repositioning of control rods within a nuclear reactor in order to maintain a critical state.
2. Description of the Related Art
Generally speaking, most nuclear fission reactors are controlled by control rods which are mechanically moved within the reactor core to control reactivity by changing the amount of neutron absorbing material in the reactor fission volume. The control rods can introduce a sufficient decrease in reactivity to control the reactor during positive reactivity transients arising from changing operating conditions. A reactivity control swing of only about one percent is typically adequate to provide control wherein the reactor can be reduced to a subcritical reactivity condition following a reactivity excursion. In routine reactor operations, an emergency insertion of the control rods is sometimes required to prevent an uncontrolled reactivity excursion.
It will be appreciated, however, that mechanical control rods have inherent limitations on the rate at which a negative reactivity can be inserted. Physical characteristics, such as inertia and rod length, limit the speed at which the control rod can be inserted into the reactor core. Further, the mechanical instability of the fuel elements in which the control rods are inserted can act to limit the insertion rate or even to preclude rod insertion.
Given this, some have proposed non-mechanical based methods for controlling the reactivity of a nuclear reaction. For example, U.S. Pat. No. 5,063,019 discloses a means for controlling the reactivity of nuclear reactors without utilizing moving mechanical means. As disclosed therein, such a method relies on the use of laser-induced polarization of Helium-3 atoms to alter the neutron absorption cross section.
Accordingly, given the above, a need exists in the art for a method that does not rely on mechanical movement to achieve control of, or supplement the control of, a nuclear reaction, or reactor.